Method and means for drilling

ABSTRACT

A method and a means for drilling in which a drilling tool is adapted to drill and to ream a flushed hole in advance of trailing casing tube means while flushing medium is returned via the casing tubes. Peripheral crushing and wedging of oversized drilling debris in the casing tube means is avoided and more efficient flushing is gained by sifting the flushing medium through a narrow slot around the tool at the mouth of the casing tube means. The slot is constantly centralized partly by a centric drill bit forwardly of eccentric reamer edges on the tool and further by the rear end of the latter being slidably supported in the casing tube means adjacent the mouth thereof.

Unite States Patent [191 Persson A METHOD AND MEANS FOR DRILLING Jan Edward Persson, Nacka, Sweden Assignee: Atlas Copco Aktiebolag, Nacka,

Sweden Filed: Feb. 1, 1973 App]. No.: 328,631

[75] Inventor:

Foreign Application Priority Data Feb. 10, 1972 Sweden 1588/72 References Cited UNITED STATES PATENTS 4/1938 Heaston .1 175/321 6/1939 Bettisn l 175/323 x 7 1939 Anderson 175 400 X 8/1945 Koppl et a1. 175/273 x Primary ExaminerJames R. Boler Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT A method and a means for driiling'in which a drilling tool is adapted to drill and to ream a flushed hole in advance of trailing casing tube means while flushing medium is returned via the casing tubes. Peripheral crushing and wedging of oversized drilling debris in the easing tube means is avoided and more efficient flushing is gained by sifting the flushing medium through a narrow slot around the tool at the mouth of the casing tube means. The slot is constantly centralized partly by a centric drill bit forwardly of eccentric reamer edges on the tool and further by the rear end of the latter being slidably supported in the casing tube means adjacent the mouth thereof.

28 Claims, 8 Drawing Figures PATENILL risv 1 91914 SHEET 3 BF 3 METHOD AND MEANS FOR DRILLING The invention relates generally to a method and a means for rotary drilling with or without the assistance of impacts. More particularly the invention relates to drilling of the above character by means of a drilling tool adapted to drill and to ream a hole in advance of casing tube means which are passed by drill rod means for carrying, rotating and supplying flushing medium to the drilling tool, the drilling particles produced during drilling being removed by the flushing medium through the casing tube means.

During drilling of the above character in sufficiently consolidated rock or soil, drilling debris and flushing.

medium may be removed through the hole outwardly of the casing tubes. The casing tubes then can be kept free from debris and soil by flushing and by a cylindrical plug at the rear end of the tool closing the mouth of the casing tube (Reference: Swedish Pat. No. 346.354). In many cases, particularly during drilling in loose overburden or soil, however, the flushing return must be conducted via the casing tubes. For allowing debris to pass it has been suggested to provide inlet openings in the form of axial grooves at the rear end of the drilling tool which is guided in the casing tube near the mouth thereof (Reference: Swedish Pat. No. 227.369). During rotation the walls in such grooves tend to provide in front of them rolling accumulations of abrasive debris from which stone particles of large size tend to be pressed into the clearance between the tool guide and the casing tube. This may cause the drilling tool to jam in the casing tube or to be torn up and destroyed. For that reason the rear end of the drilling tool usually has been made with a reduced diameter to provide considerable clearance therearound with respect to the casing tube mouth (Reference: Swedish Pat. No. 325.005). A disadvantage here is that for example eccentrically disposed cutting edges on the drilling tool, irregularities in the soil, slanting striking surfaces on stone obstacles, and the feeding force applied to the drill rod means cause the rear end thereof during rotation of the tool tosway around and to work as a particle mill against the inner wall of the casing tube. The crushing zone thus established within the mouth of the casing tube tends to produce rapid wear and failure.

It is the main object of the invention to make possible improved conditions during drilling of the above mentioned character with flushing medium return via the casing tubes by avoiding peripheral crushing and wedging of drilling particles between the drilling tool and the casing tube. Another important object in the above stated type of drilling is to improve generally the flushing of the hole during drilling in order to avoid disturbances in the drilling performance. For the above purposes there is introduced an improved centering of the drilling tool in and coaxially with respect to the casing tube string combined with a straining or sifting of the debris particles in respect of their size before they are permitted to enter into the casing tube.

SUMMARY OF THE INVENTION medium to said drilling tool, the drilling particles pro duced during drilling being removed by said flushing meduim via said casing tube means, said method comprising maintaining an annular slot of predetermined and substantially constant width between the mouth of said casing tube means and said drilling tool, and sifting the flushing medium through said slot for preventing oversized drilling particles to be entrained into said slot According to one aspect of the invention there is thus and easing tube means during removal of said flushing medium.

According to another aspect of the invention there is provided an improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises centering means on the rear portion of said drilling tool having centering surface means thereon on a diameter chosen for sliding cooperation with the interior of said casing tube means, and a cylindrical strainer body on said drilling tool forwardly of said centering means and having a diameter smaller than said centering surface means thereof for providing at the mouth of said casing tube means an annular slot therebetween and between said strainer body through which slot said flushing medium during removal is permitted to enter into said casing tube means, and bypass passage means associated with said centering means for conducting flushing medium issuing from said slot rearwardly past said surface means.

The above and other purposes of the invention will become apparent from the following description and from the accompanying drawings in which one embodiment of the invention is illustrated by way of example. It should be understood that this embodiment is only illustrative of the invention and that various modifications thereof may be made within the scope of the claims following hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS tion. FIG. 5 is a section on the line 55 in FIG. 3. FIG.

6 shows partly in section an enlarged side view of a modified embodiment of the drilling tool and the lower portion of the casing tube and drill rod means in FIG. 2. FIG. 7 is a front end view of FIG. 6. FIG. 8 shows the drilling tool in FIG. 6 during retraction through the easing tube means.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS On a tracked drilling wagon in FIG. 1 is adjustably supported a drill boom 2 which in turn carries a drilling means 3 pivotally and adjustably in two planes perpendicular to one another. The drilling means 3 comprises a feed bar 4 and a feed motor 5 which over a chain, not

shown, can displace an impact motor 6 to and fro along the feed bar 4. The impact motor 6 is associated with a rotation motor 7 which is coupled for rotating a shank adapter 8, the latter being inserted with the rear end thereof into the impact motor 6 to receive impacts therefrom.

The drill boom 2 carries a winch 10 which by a wire 11 extended over sheaves 12, 13 on the feed bar 4 is connected to a tube lifter 14. By means of a clamping ring, not shown, the lifter 14 can be fixed to a casing tube means or string 16. On the forward end of the feed bar 4 is fixed a ground stud l8 and a casing tube guide 17. The latter centralizes the casing tube means 16 axially slidably and may when need arises be fastened thereagainst in the manner of a clamping ring for gripping or braking purposes. The casing tube lifter 14 can be moved up and down along the feed bar 4 by the aid of the winsch 10 partly when it is necessary to retire or draw out the casing tube means 16, partly for lifting and positioning new casing tube sections for purposes of extending string of casing tube means by welding or threading.

A string 20 of extension drill rod means is at the upper end thereof fastened by threads to the shank adapter 8, extends through the casing tube means 16 and carries at the lower end thereof a drilling tool with a drill bit 21 thereon concentric with the drill rod means. During drilling respectively towards a cavity such as a pipe laying trench, an excavation or a mine shaft during horizontal drilling or towards a tunnel or an underground cavity during downward drilling, the centric drill bit may be given a diameter larger than the casing tube means 16. In such case drilling is performed up to the trench or cavity without retracting the drill bit. On the other hand, in more general applications when it is desired to lift the drilling tool through the casing tube means so that the latter may remain as a lining for the drilled hole, for example in a well hole, the drilling tool is preferably made as disclosed in Swedish Pat. No. 346.354. According therewith the drilling tool, FIG. 3, comprises a turnable eccentric sleeve 22 provided with reamer cutting edges 9 thereon and fitting tumably on an eccentric middle section of a shaft portion 27 which is made integral with the centric drill bit 21. During nonnal rotation the sleeve 22 is turned relative to the drill bit 21 into abutting relationship against a lug l9 thereon so as to dispose the reamer edges 9 in front of the casing tube means 16. During rotation in the opposite direction the reamer sleeve 22 is turned eccentrically 180 against another oppositely disposed abutment on the bit 21 (compare FIG. 8) whereupon the drill bit 21 and sleeve may be drawn up through the casing tube means 16 for example for inspection or regrinding. A flushing tube 23, FIGS. 4 and 5, extends coaxially through the impact motor 6 and supplies flushing medium, for example compressed air or water, to a passage 24 in the adapter 8, the rods in the drill rod means 20, and in the drilling tool for flushing the cutting edges thereof. It is preferred to adapt so called foam flushing provided by compressed air intermixed with and carrying therewith a foamed liquid composition. The flushing medium for the formation of which any suitably qualified conventional foam forming composition may be used is supplied to the flushing tube 23 via a hose. In the eccentric sleeve 22 is arranged an inner annular groove 22 supplied with flushing medium from the passage 24 through a cross bore 24 in the eccentric section of shaft 27. From the groove 22 flushing medium is passed on via a bore 22" in the sleeve 22 to flush the reamer edges 9. Another bore 22 in the sleeve 22 supplies flushing medium from the groove 22 to flush the space adjacent the lug 19 of the bit 21 in order to always assure turnability of the sleeve 22 during operation. A further bore 24 in the eccentric section of shaft 27 supplies flushing medium for flushing therear impact receiving surface of sleeve 22.

The drilling tool carries at the rear end thereof a circularly cylindrical strainer body 25 which is provided with an interior bore 26 and fits coaxially around the shaft portion 27 of the drill bit 21. A coupling sleeve 28, which may be integral with or made separate from the strainer body 25, is fixed by threads coaxially onto the shaft portion 27 and keeps the strainer body 25 in place against a shoulder on the eccentric middle portion of the shaft portion 27. The strainer body 25 has a reduced diameter such as to provide a peripheral annular slot 30 between the strainer body 25 the forward end or mouth of the casing tube means 16. The width of the slot 30 may generally be in the order of 1 3 millimeters and is preferably chosen about 2 mm. The strainer body 25 is accurately centered in the casing tube string by the aid of a centering means in FIG. 3 provided by the adjacent coupling sleeve 28. The centering may be assisted by further similar coupling sleeves 31, which by means of threads are adapted to keep together the separate extension rods of the drill rod means 20. The centering coupling sleeves 28, 31 are provided with helically extending guiding ribs 32, 33 having outer part-cylindrical centering surface means thereon. The ribs 32, 33 run in pairs axially around the coupling sleeves 28, 31 and have a total wrap angle which is sufficient for slidably guiding the coupling sleeves 28, 31peripherally on close center and in engagement with the surrounding casing tube means 16. This sliding centralizing engagement is aided by the centralizing effect of the centric drill bit 21 so that during drilling the slot 30 will be maintained constant around the strainer body 25 notwithstanding rotation of the drill rod means 20 and work of the eccentric reamer edges 9. The coupling sleeves 28 may be provided with a cross bore 34 for supplying additional flushing medium from the passage 24 of the string 20 to the bypass passage means provided by the spaces between the ribs 32, 33 and thence to the interior of the casing tube means 16. The screwing motion of the guiding ribs 32, 33 during normal working rotation of the drilling tool causes the mixture of flushing medium and drilling particles to be screwed past the coupling sleeves 28, 31 up towards the upper end of the casing tube means 16.

Referring to FIG. 4 casing tube means 16 carries at the upper end thereof a plug-like insert head 35 which in an inner bore 36 receives the flushing medium to be removed from the casing tube means 16. Further the flushing medium is deflected via a knee 37 into an emptying hose 38. In the head 35 is arranged a central bore 40 with a seal 41 which is passed slidably by the extension rods of the drill rod means 20. The shank adapter 8 is provided 'with a forward abutment face 42 by means of which the feeding movement of the impact motor 6 along the feed bar 4 and the impacts of the impact motor 6 are transmitted to the head 35 whereby the casing tube means 16 can be driven down together with and trailing immediately behind the drilling tool 21. The rotation motor 7 rotates the shank adapter 8 together with the drill rod means 20. The latter rotate freely in the bore 40 so that the casing tube means 16 is driven down without rotation.

During drilling and flushing the mixture of compressed air, foam and entrained drilling particles is pressed upwards from the drilling tool through the slot 30 and is sifted between the strainer body 25 and the mouth of the casing tube means 16 in respect of oversized debris particles which are larger than the accurately maintained width of the annular slot 30. In the subsequent restricted places for example around the extension sleeves 28, 31, therefore, the passing flushing medium mixture will contain only small debris particles of controlled maximum size which readily can pass the restrictions without causing harm. Impacting energy during drilling is transmitted through the drill rod means 20 to the sleeve 28 and then to the drill bit 21 which will produce a centric pilot bore hole. From the sleeve 28 impact energy is also transmitted via the strainer body to the eccentric sleeve 22 the edges 9 of which will ream the pilot hole to a diameter suffrcient for penetration of the casing tube means 16.

Extension of the casing tube means or string 16 is made by screwing-on or welding-on new casing tube sections which procedure is combined with simultaneous extension of the drill rod means or string 20 by screwing-on coupling sleeves and additional extension drill rods.

In the modified embodiment of FIG. 2 the feed bar 4 is provided with only a rotation motor 42. A vibration generator 43 is associated with the head 44 of the casing tube means 16 in order to improve driving of the latter. The head 44 may be clamped to the casing tube means 16 to serve as a tube lifter and is slidably moved along the feed bar 4 by the previously mentioned winch. When rotation of the drilling tool is to be assisted by impact drilling, there is applied non-rotatably at the lower end of the drill rod means 20 a conventional down-the-hole drill 45 which is centered in the casing tube means 16 by centering means provided as by guide ribs 46, 47 similar to the ones shown in FIG. 3 but sitting for example on the end cover pieces of the down-the-hole drill 45. The drilling tool 21 is similar to the one shown in FIG. 3 with an impact receiving shank projecting non rotatably into the down-the-hole drill 45 and a strainer body 25 immediately in front of the latter at the mouth of the casing tube means 16. As an alternative the foremost centering means or guide ribs 46, 47 may be provided on the rear end of the drilling tool similarly to the ribs 32, 33 in FIG. 3 but in front of the impact receivingshank received in the down-the-hole drill 45.

The shank adapter 8 abuts against the head 44 for transmitting feeding motion thereto. The shank adapter 8 also transmits rotary motion to the drill rod means 20 and to the down-the-hole drill 45. The impact motor of the down-the-hole drill 45 is driven by flushing medium comprising compressed air with foamed or finely dispersed fluid additive, and the flushing medium is supplied via a flushing tube 23 through the rotation motor 42 and the inner passage of the drill rod means 20. Flushing medium expelled from the impact motor of the down-the-hole drill is used for flushing the drilling tool. The mixture of flushing medium and drilling debris is sifted up through the accurately centralized slot in the mouth of the casing tube means 16 and then removed by continued flushing via the casing tube means.

In the modified embodiment of FIGS. 6-8 which is intended for a down-the-hole drill application similar to the one in FIG. 2, the casing tube means 16 is reinforced by a thickened mouth portion 50 providing internally an upward annular driving shoulder 51. The drill 45 has grooves and splines 52 forwardly thereon receiving the splined shank 53 of a cylindrical centering means 54. The centering means 54 comprises forwardly thereon an integral strainer body 25 and is at the rear thereof slidably centered by a cylinder surface 55 in the mouth portion 50 with the strainer body 25 protruding therefrom and defining the sifting slot 30 therearound. Between the cylinder surface 55 and the shank 53 the centering means 54 has a flange 56 thereon forming a forwardly directed shoulder 57, which cooperates with the shoulder 51 so that the impacts of the down-the-hole drill can be transmitted to the casing tube means 16. Thus the vibration generator 43 in FIG. 2 may be omitted.

When the flushing medium and debris mixture has been sifted through the slot 30 it passes an annular groove 58 in the centering means 54 and then through a plurality of substantially axial bores 59 into the casing tube means 16 for elevation and removal by continued flushing. Additional flushing medium for increasing the flushing velocity in the casing tube means 16 may be added to the groove 58 via a bore 60 which in turn is supplied with flushing medium from a central passage 61 in the centering means 54. The passage 61 receives the foam plus compressed air constituting the combined flushing and driving medium which is expelled from the impact motor of the drill 45 or internally'bypassed through the drill 45. The passage 61 also communicates with the various flushing passages of the drilling tool described in more detail in connection with FIG. 3.

I claim:

1. A method for drilling by means of a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, said method comprising a. maintaining an annular slot of predetermined and substantially constant width between the mouth of said casing tube means and said drilling tool, said slot being of a width less than the size of drilling particles which are to be blocked from entering said casing tube means,

b. keeping centering surfaces on said drilling tool in rotary sliding engagement with the interior of said casing tube means rearwardly of and in close proximity to said slot for maintaining said drilling tool on center with respect to said casing tube means and said slot width constant during drilling, and

c. sifting the flushing medium through said slot for preventing oversized drilling particles to be entrained into and churned in said slot and easing -tube means during removal of said flushing medium and rotation of said drilling tool. 2. A method according to claim 1 in which flushing medium entering through said slot is led rearwardly past said centering surfaces in bypassed relation to the sliding engagement thereof.

3. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. centering means on the rear portion of said drilling tool having centering surface means of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means,

b. a cylindrical strainer body on said drilling tool in close proximity to and forwardly of said centering means, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said centering surface means thereof for providing at the mouth of said casing tube means an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, and

c. bypass passage means associated with said centering surface means for conducting flushing medium issuing from said slot rearwardly past said centering surface means in bypassed relation to the sliding engagement thereof.

4. A drilling means according to claim 3 in which said drilling tool comprises a drill bit with an integral shaft portion coaxial therewith and in fixed coaxial engagement with said strainer body and centering means.

5. A drilling means according to claim 4 in which said drilling tool comprises a sleeve mounted on said shaft between said strainer body and said drill bit, and reamer cutting edge means for said casing tube means, said cutting edge means being provided on said sleeve.

6. A drilling means according to claim 5 in which said shaft has an eccentric portion and said sleeve is mounted on said eccentric portion of said shaft turnably between diametrically opposed positions, and peripherally spaced abutment means for said sleeve on said drill bit for defining said diametrically opposed positions, said abutment means maintaining said sleeve with said cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.

7. A drilling means according to claim 6 in which there are provided cooperating impact transmitting surfaces on said strainer body and said sleeve, one of the abutment means of said drill bit being slanted for urging the abutting surface of said sleeve against the abutting surface of said strainer body during appropriate rotation of said drilling tool.

8. A drilling means according to claim 4 in which said centering means comprises a coupling sleeve in threaded engagement with said drill rod means and said shaft portion, said centering surface means being disposed on helically extending guiding ribs defining said bypass passage means therebetween and disposed on and extending from said coupling sleeve with a suffis ciently large wrap angle so as to provide radial guidance of said coupling sleeve on center with the surrounding casing tube means.

9. A drilling means according to claim 4 in which said centering means comprises a cylindrical body with said centering surface means provided cylindrically therearound, an annular groove between said cylindrical body and said strainer body, and bypass passage means for said flushing medium extending rearwardly from said groove through said cylindrical body.

10. A drilling means according to claim 4 in which a splined impact receiving shank is provided integrally with said centering means, and a down-the-hole drill is disposed at the head of said drill rod means in said casing tube means for carrying, rotating, supplying flushing medium and impacting said drilling tool means by said shank.

11. A drilling means according to claim 10 in which said casing tube means has an internal shoulder spaced rearwardly from the mouth thereof, and said centering means is provided with a shoulder thereon for impact transmitting cooperation with said internal shoulder in said casing tube means.

12. A drilling means according to claim 3 in which said drilling tool comprises a drill bit having an integral rearwardly extending shaft portion, said rearwardly ex tending shaft portion of said drill bit being in axially fixed coaxial engagement with said strainer body, a sleeve mounted eccentrically on said shaft portion between said strainer body and said drill bit, and reamer cutting edges on said sleeve.

13. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. a drill bit having a shaft which extends rearwardly therefrom,

b. a sleeve mounted on an intermediate portion of said shaft,

c. eccentrically disposed reamer cutting edge means on said sleeve,

d. a cylindrical strainer body disposed on the rear end of said shaft in coaxial relation to said drill bit, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said mouth for providing an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, said strainer slot being dimensioned so as to block large size drilling particles from entering said casing tube means,

e. centering means in coaxial proximity rearwardly of said strainer body, said centering means having centering surface means of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means, and

f. bypass passage means associated with said centering surface means for conducting flushing medium issuing from said slot rearwardly past said centering surface means in bypassed relation to the sliding engagement thereof.

14. A drilling means according to claim 13 in which said intermediate portion of said shaft is disposed eccentrically to said drill bit and said sleeve is mounted turnably thereon between diametrically opposed positions, and said drilling means including spaced abutment means on said drill bit for defining said positions of said sleeve, said abutment means maintaining said sleeve with said reamer cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.

15. A drilling means according to claim 14 in which there are provided cooperating axial faces on said strainer body and said sleeve for transmitting impacts therebetween, one of said abutment means of said drill bit being slanted for urging the abutting surface of said sleeve against the abutting surface of said strainer body during appropriate rotation of said drilling tool.

16. A drilling means according to claim 13 in which said centering means comprises a coupling sleeve adapted for threaded engagement with said drill rod means and said shaft portion, helically extending guiding ribs on said sleeve defining said bypass passage means therebetween, said centering surface means terminating said ribs in a radial direction, and said ribs defining a sufficiently large wrap angle for said surface means so as to provide close radial guidance of said coupling sleeve in sliding relation on center with the surrounding casing tube means.

17. A drilling means according to claim 13 in which said centering means comprises a cylindrical body with said centering surface means provided cylindrically therearound, an annular groove between said cylindrical body and said strainer body, and bypass passage means for said flushing medium extending rearwardly from said groove through said cylindrical body.

18. A drilling means according to claim 13 in which a splined impact receiving shank is provided integrally with said centering means, and a down-the-hole drill is disposed at the head of said drill rod means in said casing tube means for carrying, rotating, supplying flushing medium and impacting said drilling tool means by said shank.

19. A drilling means according to claim 18 in which there is provided an internal shoulder in said casing tube means spaced rearwardly from the mouth thereof and said centering means is provided with a shoulder thereon for impact transmitting cooperation with said internal shoulder.

20. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. a ring shoulder at the forward end mouth of said casing tube means, said mouth of said casing tube means being drill bit free,

b. a down-the-hole drill in said casing tube means,

c. a cylindrical guide flange cooperating coaxially and slideably with the inside of said casing tube means,

d. a shank piece extending from said cylindrical guide flange and in striking engagement with said downthe-hole drill, said cylindrical guide flange hitting said ring shoulder under impacts of said down-thehole drill for feeding the drill-bit-free forward end of the casing tube means under said impacts, and

e. drill bit means connected to and forwardly of said I cylindrical guide flange for drilling a hole in advance of said casing tube means.

21. A drilling means according to claim 20 wherein said shank piece and down-the-hole drill are matingly splined.

22. A drilling means according to claim 20 in which said drill bit means has a shaft which extends rearwardly from a drill bit to couple said drill bit to said cylindrical guide flange, and further comprising a cylin' drical strainer body disposed on the rear end of said shaft in coaxial relation to said drill bit, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said mouth for providing an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, said strainer slot being dimensioned so as to block large size drilling particles from entering said casing tube means.

23. A drilling means according to claim 22 including a sleeve mounted on an intermediate portion of said shaft, and eccentrically disposed reamer cutting edge means on said sleeve.

24. A drilling means according to claim 23 wherein said sleeve is mounted eccentrically on said shaft.

25. A drilling means according to claim 24 wherein said shaft has an eccentric intermediate portion and said sleeve is mounted on said eccentric portion.

26. A drilling means according to claim 23 in which said intermediate portion of said shaft is disposed eccentrically to said drill bit and said sleeve is mounted tumably thereon between diametrically opposed positions, and said drilling means including spaced abutment means on said drill bit for defining said positions of said sleeve, said abutment means maintaining said sleeve with said reamer cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.

27. A drilling means according to claim 20 including centering means in coaxial proximity rearwardly of said strainer body, said centering means having centering surface mean of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means.

28. A drilling means according to claim 27 wherein said centering means includes said cylindrical guide flange which is integral with said shank piece. 

1. A method for drilling by means of a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, said method comprising a. maintaining an annular slot of predetermined and substantially constant width between the mouth of said casing tube means and said drilling tool, said slot being of a width less than the size of drilling particles which are to be blocked from entering said casing tube means, b. keeping centering surfaces on said drilling tool in rotary sliding engagement with the interior of said casing tube means rearwardly of and in close proximity to said slot for maintaining said drilling tool on center with respect to said casing tube means and said slot width constant during drilling, and c. sifting the flushing medium through said slot for preventing oversized drilling particles to be entrained into and churned in said slot and casing tube means during removal of said flushing medium and rotation of said drilling tool.
 2. A method according to claim 1 in which flushing medium entering through said slot is led rearwardly past said centering surfaces in bypassed relation to the sliding engagement thereof.
 3. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. centering means on the rear portion of said drilling tool having centering surface means of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means, b. a cylindrical strainer body on said drilling tool in close proximity to and forwardly of said centering means, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said centering surface means thereof for providing at the mouth of said casing tube means an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, and c. bypass passage means associated with said centering surface means for conducting flushing medium issuing from said slot rearwardly past said centering surface means in bypassed relation to the sliding engagement thereof.
 4. A drilling means according to claim 3 in which said drilling tool comprises a drill bit with an integral shaft portion coaxial therewith and in fixed coaxial engagement with said strainer body and centering means.
 5. A drilling means according to claim 4 in which said drilling tool comprises a sleeve mounted on said shaft between said strainer body anD said drill bit, and reamer cutting edge means for said casing tube means, said cutting edge means being provided on said sleeve.
 6. A drilling means according to claim 5 in which said shaft has an eccentric portion and said sleeve is mounted on said eccentric portion of said shaft turnably between diametrically opposed positions, and peripherally spaced abutment means for said sleeve on said drill bit for defining said diametrically opposed positions, said abutment means maintaining said sleeve with said cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.
 7. A drilling means according to claim 6 in which there are provided cooperating impact transmitting surfaces on said strainer body and said sleeve, one of the abutment means of said drill bit being slanted for urging the abutting surface of said sleeve against the abutting surface of said strainer body during appropriate rotation of said drilling tool.
 8. A drilling means according to claim 4 in which said centering means comprises a coupling sleeve in threaded engagement with said drill rod means and said shaft portion, said centering surface means being disposed on helically extending guiding ribs defining said bypass passage means therebetween and disposed on and extending from said coupling sleeve with a sufficiently large wrap angle so as to provide radial guidance of said coupling sleeve on center with the surrounding casing tube means.
 9. A drilling means according to claim 4 in which said centering means comprises a cylindrical body with said centering surface means provided cylindrically therearound, an annular groove between said cylindrical body and said strainer body, and bypass passage means for said flushing medium extending rearwardly from said groove through said cylindrical body.
 10. A drilling means according to claim 4 in which a splined impact receiving shank is provided integrally with said centering means, and a down-the-hole drill is disposed at the head of said drill rod means in said casing tube means for carrying, rotating, supplying flushing medium and impacting said drilling tool means by said shank.
 11. A drilling means according to claim 10 in which said casing tube means has an internal shoulder spaced rearwardly from the mouth thereof, and said centering means is provided with a shoulder thereon for impact transmitting cooperation with said internal shoulder in said casing tube means.
 12. A drilling means according to claim 3 in which said drilling tool comprises a drill bit having an integral rearwardly extending shaft portion, said rearwardly extending shaft portion of said drill bit being in axially fixed coaxial engagement with said strainer body, a sleeve mounted eccentrically on said shaft portion between said strainer body and said drill bit, and reamer cutting edges on said sleeve.
 13. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill rod means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. a drill bit having a shaft which extends rearwardly therefrom, b. a sleeve mounted on an intermediate portion of said shaft, c. eccentrically disposed reamer cutting edge means on said sleeve, d. a cylindrical strainer body disposed on the rear end of said shaft in coaxial relation to said drill bit, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said mouth for providing an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, said strainer slot being dimensioned so as to block large size drilling partIcles from entering said casing tube means, e. centering means in coaxial proximity rearwardly of said strainer body, said centering means having centering surface means of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means, and f. bypass passage means associated with said centering surface means for conducting flushing medium issuing from said slot rearwardly past said centering surface means in bypassed relation to the sliding engagement thereof.
 14. A drilling means according to claim 13 in which said intermediate portion of said shaft is disposed eccentrically to said drill bit and said sleeve is mounted turnably thereon between diametrically opposed positions, and said drilling means including spaced abutment means on said drill bit for defining said positions of said sleeve, said abutment means maintaining said sleeve with said reamer cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.
 15. A drilling means according to claim 14 in which there are provided cooperating axial faces on said strainer body and said sleeve for transmitting impacts therebetween, one of said abutment means of said drill bit being slanted for urging the abutting surface of said sleeve against the abutting surface of said strainer body during appropriate rotation of said drilling tool.
 16. A drilling means according to claim 13 in which said centering means comprises a coupling sleeve adapted for threaded engagement with said drill rod means and said shaft portion, helically extending guiding ribs on said sleeve defining said bypass passage means therebetween, said centering surface means terminating said ribs in a radial direction, and said ribs defining a sufficiently large wrap angle for said surface means so as to provide close radial guidance of said coupling sleeve in sliding relation on center with the surrounding casing tube means.
 17. A drilling means according to claim 13 in which said centering means comprises a cylindrical body with said centering surface means provided cylindrically therearound, an annular groove between said cylindrical body and said strainer body, and bypass passage means for said flushing medium extending rearwardly from said groove through said cylindrical body.
 18. A drilling means according to claim 13 in which a splined impact receiving shank is provided integrally with said centering means, and a down-the-hole drill is disposed at the head of said drill rod means in said casing tube means for carrying, rotating, supplying flushing medium and impacting said drilling tool means by said shank.
 19. A drilling means according to claim 18 in which there is provided an internal shoulder in said casing tube means spaced rearwardly from the mouth thereof and said centering means is provided with a shoulder thereon for impact transmitting cooperation with said internal shoulder.
 20. An improved drilling means of the type incorporating a rotatable drilling tool adapted to drill a hole in advance of trailing casing tube means which are passed by rotatable drill means for carrying, rotating, and supplying flushing medium to said drilling tool, the drilling particles produced during drilling being removed by said flushing medium via said casing tube means, wherein the improvement comprises a. a ring shoulder at the forward end mouth of said casing tube means, said mouth of said casing tube means being drill bit free, b. a down-the-hole drill in said casing tube means, c. a cylindrical guide flange cooperating coaxially and slideably with the inside of said casing tube means, d. a shank piece extending from said cylindrical guide flange and in striking engagement with said down-the-hole drill, said cylindrical guide flange hitting said ring shoulder under impacts of said down-the-hole drill for feeding the drill-bit-free forward end of the casing tube means under said impacts, and e. drill bit means connected to and forwardly of said cylindrical guide flange for drilling a hole in advance of said casing tube means.
 21. A drilling means according to claim 20 wherein said shank piece and down-the-hole drill are matingly splined.
 22. A drilling means according to claim 20 in which said drill bit means has a shaft which extends rearwardly from a drill bit to couple said drill bit to said cylindrical guide flange, and further comprising a cylindrical strainer body disposed on the rear end of said shaft in coaxial relation to said drill bit, said strainer body protruding from the mouth of said casing tube means and having a diameter smaller than said mouth for providing an annular strainer slot between said strainer body and said casing tube means through which slot said flushing medium during removal is permitted to enter into said casing tube means, said strainer slot being dimensioned so as to block large size drilling particles from entering said casing tube means.
 23. A drilling means according to claim 22 including a sleeve mounted on an intermediate portion of said shaft, and eccentrically disposed reamer cutting edge means on said sleeve.
 24. A drilling means according to claim 23 wherein said sleeve is mounted eccentrically on said shaft.
 25. A drilling means according to claim 24 wherein said shaft has an eccentric intermediate portion and said sleeve is mounted on said eccentric portion.
 26. A drilling means according to claim 23 in which said intermediate portion of said shaft is disposed eccentrically to said drill bit and said sleeve is mounted turnably thereon between diametrically opposed positions, and said drilling means including spaced abutment means on said drill bit for defining said positions of said sleeve, said abutment means maintaining said sleeve with said reamer cutting edge means thereof respectively radially projected or retracted with respect to said strainer body.
 27. A drilling means according to claim 20 including centering means in coaxial proximity rearwardly of said strainer body, said centering means having centering surface mean of substantial axial width thereon on a diameter chosen for sliding engagement with an interior cylindrical portion of said casing tube means.
 28. A drilling means according to claim 27 wherein said centering means includes said cylindrical guide flange which is integral with said shank piece. 